Electronic control circuits are known in many designs. In the case of the preferred configuration, as the commutation electronic device of an EC motor, i.e. a brushless, electronically commutated electric motor, four or six power transistors are connected to a bridged power amplifier as a rule, the power amplifier being supplied from a DC voltage intermediate circuit. The individual power transistors are controlled by a control unit such that the motor windings are controlled in a manner dependent on the rotational position of a rotor in such a way that a rotating magnetic field to rotate the rotor is created. In this respect the power amplifier practically acts as an inverter, it also being possible for PWM clocking to take place for speed adjustment.
Control circuits are also known generally as inverters or frequency converters for other uses.
The power transistors can either be arranged as discrete components on a support, e.g. a circuit board, or integrated into a module on a common substrate. Moreover, they can be arranged on a heatsink and be designed as bipolar transistors, IGBT's or MOSFET's, for example.
Theoretically, semiconductor elements are not subject to any restriction of service life. In practice, however, ageing processes and total failures of power transistors do occur, i.e. semiconductor components have a finite service life in practical use from experience.